Variable focus liquid lenses are known in the art. Such lenses generally comprise a refractive interface between first and second immiscible liquids that is moveable by electrowetting. FIG. 1 reproduces FIG. 4 of European Patent Application EP1662276, and illustrates a known variable focal length lens 10. Lens 10 comprises two transparent windows 24, 38 facing each other and parallel to one another, and delimiting, at least in part, an internal volume 15 containing two immiscible liquids 16, 18, with different optical indices, defining an optical interface A, B in the form of a meniscus where they meet. The liquids 16, 18 have substantially equal densities, and one is preferably an insulating liquid, for example comprising oil or an oily substance, and the other is preferably a conducting liquid comprising for example an aqueous solution. The windows are for example transparent plates, made of an optical transparent material, e.g. glass. Whilst planar windows are shown, these windows could be fixed lens, centred on an optical axis (Δ) of the variable focus lens 10.
Lens 10 further comprises a cap 30 connected to transparent window 38 and comprising a first cylindrical side wall 34. Lens 10 also comprises a body 16 having a symmetry of revolution about the optical axis (Δ) of the lens. Body 16 is connected to transparent window 24 and comprises a second cylindrical side wall 20 of a diameter smaller than the diameter of the first cylindrical wall. Cap 30 forms a first electrode and body 16 comprises a second electrode. A gasket 50 is provided to ensure the tightness of the lens structure, positioned such that it is compressed between the first and second cylindrical side walls. In particular, gasket 50 is substantially “L”-shaped in cross-section, comprising a portion 54 compressed between the first and second cylindrical side walls and a portion 52 compressed between the cap and a top surface 42 of body 12, the top surface 42 comprising an opening defining a conical or cylindrical surface 48 where the interface between the two liquids is able to move.
The lens further comprises deforming portions 36 arranged to deform in response to a change in pressure of the liquids. The deforming portions for example comprise corrugated regions 36 formed in the upper wall 31 of the cap, the deforming portions having symmetry of revolution about the optical axis (Δ) of the lens. For example, the deforming portions comprise at least one circular ripple centred on the optical axis (Δ) of the lens. In this example the cap is for example made of a stamped metal, pressed into shape, e.g. stamped stainless steel. The thickness of the upper wall of the cap will depend on the expected variations of volume to compensate for the effects of expansion of the liquids. For example, a typical thickness of about 0.1 to 0.25 mm has shown good results for lenses whose outer diameters is below 20 mm.
Side wall 34 of the cap comprises a rim 56 crimped onto the body 16, which deforms the gasket 50 between the cap and a corner of body 16, and seals the cap and the body. Other methods for sealing the cap onto the body are possible, for example it would be possible to glue the cap onto the body.
Due to the electrowetting effect, it is possible, by applying a voltage between the cap 30 and base 16, to change the curvature of the refractive interface between the first liquid 106 and the second liquid 108, for example, from an initial concave shape as shown by dashed line A, to a convex shape as shown by solid line B. Thus rays of light passing through the cell perpendicular to the windows 24, 38 in the region of the refractive interface A, B will be focused more or less depending on the voltage applied.
When a variable focus liquid device, for example the device of FIG. 1, is to be mounted in a digital camera, mobile phone or the like, it is necessary to connect the electrodes of the variable lens to driving circuitry that provides the appropriate drive voltages to control the lens. Depending on the positioning of the variable lens with respect to the driving circuitry, a relatively significant gap is required to be bridged to make this connection. Whilst flexible conducting wires could be used to connect the electrodes of the lens to the drive circuitry, these are disadvantageous as they are bulky, and can cause interference with other components close by. There is thus a need for a low cost interconnection that requires minimal space and causes little or no interference with nearby components.